This invention is directed to an abrasive material, prepared from a steel plant waste product, which can be used as a substitute for mineral abrasives or sand to manually blast clean the surface of ferrous metals prior to painting.
Sand is the oldest abrasive which has been used to remove contaminants from the surface of ferrous metals. Sand is plentiful, hard, efficient and relatively cheap. However, sand is brittle and has a high breakdown rate when impacted at high velocity on the surface which is being blast cleaned. Small discrete particles of sand are produced, forming large volumes of dust. Vision is thus impaired during cleaning. The particles of dust settle on the surface being cleaned and on all adjacent areas, necessitating major cleanup of the blasted surface and the adjacent areas after blasting. It is, as a consequence, necessary to protect all surrounding machinery and operators. Sand is essentially silica. Continued inhalation of the discrete small particles of sand can cause silicosis. As a result, substitute abrasives for sand have been sought.
Both metallic and non-metallic abrasives have been developed to replace sand. Metallic abrasives are produced by special processes. The abrasives are hard and tough and have long breakdown rates. However, metallic abrasives are expensive and are generally limited to indoor or protected corrosion free atmospheres wherein the particles can be reclaimed and recycled between 50 and 5,000 times so that their use is economically feasible.
Mineral or non-metallic abrasives are generally less dense and lighter and more brittle than metallic abrasives. Mineral abrasives generally are similar to sand and have a high breakdown rate. They are used in the same applications as sand, i.e. applications in which the abrasives are not reclaimed. Because of their high breakdown rate, large volumes of dust are generated when manually blast cleaning ferrous surfaces. Many of the mineral abrasives contain silica and are more or less toxic. Because of their high breakdown rate it is necessary to clean the blasted surface and surrounding areas to remove excess dust. Mineral abrasives are packaged in narrow size ranges, hence one size of an abrasive is used to remove coarse contaminants and another size is used to remove light contaminants. A mixture of two sizes of mineral abrasives is required to clean both coarse and light contaminants at the same time. However, this practice can and does result in folded-in dirt and rust on the blasted surface.
Scarfer spittings are a waste product produced in steel preparation shops. Scarfing is defined as a process for removing surface defects from ingots, billets, bars, etc. by means of a gas torch. Scarfer spittings are spherical-like waste particles ranging in size from +2 inches to less than 100 mesh sieve size formed during scarfing. The scarfer spittings are initially molten steel and are usually quenched in water to cool before handling. Scarfer spittings contain a metallic iron core and a shell of iron oxides surrounding the core. Because of the presence of iron it has been proposed to use the scarfer spittings as part of the charge to sintering machines. In fact a small percentage of scarfer spittings are so used. Attempts to reclaim the iron in scarfer spittings along with other in-plant waste materials such as mill scale and fume to make heat hardened pellets suitable for charging into metallurgical furnaces have not been commercially successful. Since the quantity of scarfer spittings which are reclaimed is relatively small, it is necessary to store them when they are removed from the steel plants or else discard them. Both handling and storage are expensive in terms of labor and storage area.